DESCRIPTION: (Applicant's Description) The overall goal of this project is to study the dosimetric basis of optimized conformal and IMRT treatment delivery, and to evaluate the dosimetric results which are possible to achieve with optimization of the various conformal delivery techniques which are available. The dose delivered to the patient (with any delivery technology) is the key to the outcome obtained by the patient, so this project concentrates on the study of various aspects of the dose distributions planned and/or achieved with different conformal therapy techniques, including static conformal and intensity modulated radiation therapy (IMRT). Modern conformal therapy, especially conformal therapy based on IMRT, often makes use of automated optimization software to assist in the creation of the treatment plan to be delivered, and study of the dosimetric aspects of this optimization process is an important component of this project. Both the optimization process and accurate dose calculation algorithms are extremely computationally intensive, so approximations are required. This project will compare and evaluate results of optimization sequences in which intensity distributions are optimized versus those in which the actual dose distribution is optimized. The project will also compare and evaluate the dosimetric and other capabilities of various delivery strategies, including multiple conformally- shaped fields, multiple segment IMRT, IMRT created with dynamic MLC control, checkerboard-like intensity distributions, specialized MLC or multivane collimator systems, and scanned beam electrons. The final dosimetric issue studied involves patient-specific dosimetric issues for conformal/IMRT delivery, including inhomogeneities and surface-buildup region issues. Knowledge of the dosimetric influence these different issues have on the plan optimization process may help minimize the complexity of optimization and treatment strategies, determine realistic limits to improvements any planning or delivery method will allow, and guide the field as it considers use of various methodologies for particular clinical problems.